Polyester polymer particles having a small surface to center molecular weight gradient

ABSTRACT

There is now provided a polyester polymer particle having an It.V., a surface, and a center, wherein the It.V. at the surface of the particle is less than 0.25 dL/g higher than the It.V. at the center of the particle. The polyester polymer particle is desirably crystalline to prevent the particles from sticking to each other while drying, and desirably contains less than 10 ppm acetaldehyde. A polyester container, preferably a preform or beverage bottle, is made by feeding crystallized polyester particles having an It.V. of at least 0.70 dL/g to an extrusion zone, melting the particles in the extrusion zone to form a molten polyester polymer composition, and forming a sheet or a molded part from extruded molten polyester polymer, wherein at least a portion of the polyester particles have an It.V. at their surface which does not vary from their It.V. at their center by more than 0.25 dL/g, and the particles have not been solid state polymerized. Such polyester compositions have an It.V. suitable for containers, yet lose less It.V. during melt processing than existing polyesters.

1. FIELD OF THE INVENTION

This invention relates to polyester polymer pellets suitable for use inthe manufacture of polyester containers, and more specifically, topolyester polymer particles having a small surface to center molecularweight gradient.

2. BACKGROUND OF THE INVENTION

Polyester polymer pellets, and in particular polyethylene terephthalatehomopolymers and copolymers (PET), experience a loss of intrinsicviscosity (It.V.) during melt processing in, for example, an injectionmolding extruder. As a result of losing It.V., the physical propertiesof the polymer also degrade. One cause of It.V. loss is the hydrolyticdegradation of the polymer caused by water absorbed in the polymer priorto melt processing. To prevent hydrolysis, the polymer is thoroughlydried prior to melt processing. While drying the polymer reduces theloss of It.V., nevertheless, some drop in It.V. is experienced, therebyrequiring the use of a polymer having an It.V. higher than the targetcontainer It.V. to compensate for It.V. losses during extrusion. The useof higher than target It.V. polymers has the added disadvantage ofhigher costs due to more energy consumption required to heat the polymerfor a longer time and to agitate a more viscous material, and/or due tothe extension of the residence time during melt phase polymerization tobring the It.V. up to the desired level, resulting in a decreasedproduction rate. The use of higher than target It.V. polyester polymersalso has the disadvantage of requiring more energy to feed the polymeralong the screw in the extruder.

It would be desirable to reduce the loss in It.V. experienced by thepolyester polymer during melt processing for making containers.

3. SUMMARY OF THE INVENTION

We have discovered a polyester composition that has an It.V. suitablefor containers, yet loses less It.V. during melt processing thanexisting polyesters.

There is now provided a polyester polymer particle comprising apolyester polymer comprising:

-   -   (a) a carboxylic acid component comprising at least 90 mole % of        the residues of terephthalic acid, derivates of terephthalic        acid, naphthalene-2,6-dicarboxylic acid, derivatives of        naphthalene-2,6-dicarboxylic acid, or mixtures thereof, and    -   (b) a hydroxyl component comprising at least 90 mole % of the        residues of ethylene glycol,        based on 100 mole percent of the carboxylic acid component        residues and 100 mole percent hydroxyl component residues in the        polyester polymer, wherein said particle has an It.V. of at        least 0.7 dL/g , and the It.V. at the surface of the particle is        less than 0.25 dL/g higher than the It.V. at the center of the        particle.

There is also provided a polyester particle having a degree ofcrystallinity of at least 25% and an It.V. of at least 0.70 dL/g , saidparticle having an It.V. at its surface and an It.V. at its center,wherein the It.V. at the surface of the particle is less than 0.25 dL/ghigher than the It.V. at the center of the particle.

In addition, there is provided a process for making a polyestercontainer, comprising feeding polyester particles having a degree ofcrystallinity of at least 15% and an It.V. of at least 0.70 dL/g to anextrusion zone, melting the particles in the extrusion zone to form amolten polyester polymer composition, and forming a sheet or a moldedpart from extruded molten polyester polymer, wherein the polyesterparticles fed to the extrusion zone have an It.V. at their surface whichis less than 0.25 dL/g higher than the It.V. at their center.

In yet another embodiment, there is provided polyester particles havinga particle weight of greater than 1.0 g per 100 particles and less than100 g per 100 particles, said particles comprising at least 75% virginpolyester polymer comprising:

-   -   (a) a carboxylic acid component comprising at least 90 mole % of        the residues of terephthalic acid, or derivates of terephthalic        acid, or mixtures thereof, and    -   (b) a hydroxyl component comprising at least 90 mole % of the        residues of ethylene glycol,

-   based on 100 mole percent of the carboxylic acid component residues    and 100 mole percent hydroxyl component residues in the polyester    polymer, the particles having a degree of crystallinity of at least    25%, an It.V. of at least 0.77 dL/g, an It.V. at their surface and    an It.V. at their center wherein the It.V. at the surface of the    particles is not greater than 0.15 dL/g higher than the It.V. at the    center of the particles, and having an acetaldehyde level of 10 ppm    or less.

4. DETAILED DESCRIPTION OF THE INVENTION

The present invention may be understood more readily by reference to thefollowing detailed description of the invention and the examplesprovided therein. It must also be noted that, as used in thespecification and the appended claims, the singular forms “a,” “an” and“the” include plural referents unless the context clearly dictatesotherwise. For example, reference to processing or making a “polymer,” a“particle,” “preform,” “article,” “container,” or “bottle” is intendedto include the processing or making of singular and a plurality ofpolymers, preforms, articles, containers or bottles. References to acomposition containing “an” ingredient or “a” polymer is intended toinclude other ingredients or other polymers, respectively, in additionto the one named.

By “comprising” or “containing” is meant that at least the namedcompound, element, particle, or method step etc must be present in thecomposition or article or method, but does not exclude the presence ofother compounds, catalysts, materials, particles, method steps, etc,even if the other such compounds, material, particles, method steps etc.have the same function as what is named, unless expressly excluded inthe claims.

It is also to be understood that the mention of one or more method stepsdoes not preclude the presence of additional method steps before orafter the combined recited steps or intervening method steps betweenthose steps expressly identified. Moreover, the lettering of processsteps is a convenient means for identifying discrete activities orsteps, and unless otherwise specified, recited process steps can bearranged in any sequence. Moreover, unless specifically stated, therecited steps can be carried out in any sequence.

A stated range includes all integers and fractions thereof within therange.

A polyester polymer composition is any thermoplastic polyester polymerin any state (e.g. solid or molten), and in any shape, each as thecontext in which the phrase is used dictates, and includes thecomposition of matter resulting from the melt phase, or as a solid, orthe molten composition of matter in an extrusion zone, a sheet or bottlepreform, or in the form of a stretch blow molded bottle. The polyesterpolymer composition may contain any type and number of additives.

The intrinsic viscosity values described throughout this description todescribe the pellet It.V. are set forth in dL/g units as calculated fromthe inherent viscosity measured at 25° C. in 60/40 wt/wtphenol/tetrachloroethane.

The It.V. of the pellets is determined by measuring the weight-averagemolecular weight of the polyester by gel permeation chromatography (GPC) from which the It.V. can be calculated as described below. The GPCanalysis is used to estimate the molecular weight of the polyesterpellets for determining the molecular weight gradient from the surfaceto the center of the particles:

-   -   Solvent: 95/5 by volume methylene chloride/hexafluoroisopropanol    -   +0.5 g/L tetraethylammonium bromide    -   Temperature: ambient    -   Flow rate: 1 mL/min    -   Sample Solution:    -   4 mg polyester polymer in 10 mL methylene        chloride/hexafluoroisopropanol azeotrope (˜70/30 by vol)+10 μl        toluene flow rate marker. For filled materials, the sample mass        is increased so that the mass of polymer is about 4 mg, and the        resulting solution is passed through a 0.45 μm Teflon filter.    -   Injection volume: 10 μL    -   Column set: Polymer Laboratories 5 μm PLgel, Guard+Mixed C    -   Detection: UV absorbance at 255 nm    -   Calibrants: monodisperse polystyrene standards, MW=580 to        4,000,000 g/mole, where MW is the peak molecular weight    -   Universal calibration parameters:        PS K=0.1278 a=0.7089        PET K=0.4894 a=0.6738    -   The universal calibration parameters are determined by linear        regression to yield the correct weight average molecular weights        for a set of five polyester polymer samples previously        characterized by light scattering.    -   The calculation of inherent viscosity at 0.5 g/dL in 60/40        phenol/tetrachloroethane from the weight-average molecular        weight, <M>_(w), is determined as follows:        Ih.V.=4.034×10⁻⁴ <M> _(w) ^(0.691)    -   The intrinsic viscosity (It.V. or η_(int)) may then be        calculated from the inherent viscosity using the Billmeyer        equation as follows:        It.V.=0.5[e^(0.5×Ih.V.)−1]+(0.75×Ih.V.)

The solution viscosity relates to the composition and molecular weightof a polyester polymer. Although the IhV numbers for the crystallizedproducts to determine the molecular weight gradient are calculated byGPC, solution viscosity measurements are made to determine the It.V. ofthe pellets and preforms. The following equations describe such solutionviscosity measurements and subsequent calculations:η_(inh) =[In (t _(s) /t_(o))]/Cwhere η_(inh)=Inherent viscosity at 25° C. at a polymer concentration of0.50 g/100 mL of 60% phenol and 40% 1,1,2,2-tetrachloroethane

-   -   In=Natural logarithm    -   t_(s)=Sample flow time through a capillary tube    -   t_(o)=Solvent-blank flow time through a capillary tube    -   C=Concentration of polymer in grams per 100 mL of solvent        (0.50%)_(—)

The intrinsic viscosity is the limiting value at infinite dilution ofthe specific viscosity of a polymer. It is defined by the followingequation:$\eta_{int} = {{\lim\limits_{C\rightarrow 0}\left( {\eta_{sp}/C} \right)} = {\lim\limits_{C\rightarrow 0}\quad{\ln\left( {\eta_{r}/C} \right)}}}$where η_(int)=Intrinsic viscosity

-   -   η_(r)=Relative viscosity=t _(s) /t_(o)    -   η_(sp)=Specific viscosity=η_(r)−1

Instrument calibration involves replicate testing of a standardreference material and then applying appropriate mathematical equationsto produce the “accepted” I.V. values.Calibration Factor=Accepted IV of Reference Material/Average ofReplicate DeterminationsCorrected IhV=Calculated IhV×Calibration Factor

The intrinsic viscosity (ItV or η_(int)) may be estimated using theBillmeyer equation as follows:η_(int)=[e^(0.5×Corrected IhV)−1]+(0.75×Corrected IhV)

There is now provided a polyester polymer particle having an It.V. of atleast 0.75 dL/g , a surface, and a center, wherein the It.V. at thesurface of the particle is not greater than 0.25 dL/g higher than theIt.V. at the center of the particle, preferably not greater than 0.20dL/g higher than the It.V. at the center of the particle. There is alsoprovided a polyester polymer particle having an It.V. of at least 0.75dL/g , a surface, and a center, wherein the It.V. of the particle at thesurface is greater than the It.V. of the particle at its center by notmore than 0.25 dL/g, preferably by no more than 0.20 dL/g.

The polyester particles are solid at 25° C. and 1 atmosphere. The shapeof the particles is not limited. Suitable shapes include spheres, cubes,pellets, chips, pastilles, stars, and so forth. The particles have anumber average weight of at least 0.10 g per 100 particles, morepreferably greater than 1.0 g per 100 particles, and up to about 100 gper 100 particles. The volume of the particles is not particularlylimited, but in one embodiment, there is provided a bulk of particleshaving a volume of at least 1 cubic meter, or at least 3 cubic meters.For example, one or more random samplings of 10 or more particles in abulk of at least 1 cubic meter will yield the small surface to centerIt.V. gradient of the invention. Therefore, in a further embodiment, theaverage It.V. gradient in a bulk of particles having a volume of 1 cubicmeter or more is small as set forth in this description.

The It.V. of the polyester particles is suitable for containerapplications. The It.V. of the polyester particles is at least 0.70dL/g. For example, the It.V. of the polyester particles can be at least0.75, or 0.77, or 0.80 dL/g, and up to about 1.2 dL/g, or 1.1 dL/g. Thepolyester particles fed to an injection molding machine are desirablynot subjected to an increase in their molecular weight in the solidstate.

The polyester particles have a small surface to center molecular weightgradient between the surface and the center of the particles than foundin solid-stated polyester particles. Without being bound to a theory, itis believed that when there is a significant difference in It.V. betweenthe center and surface of the polyester particle, as in the case of asolid-stated polyester particle, and such a polymer is melted, thepolymer chains undergo chemical reactions that equilibrate the molecularweight distribution. Even when the number-average molecular weight isunaffected, the equilibration causes the It.V. and weight-averagemolecular weight to decrease, which also causes a degradation of thephysical properties of the polyester. Accordingly, by melt processing apolyester particle having a smaller surface to center molecular weightgradient, the loss in It.V. is reduced.

The polyester polymer particles have a surface and a center, and theIt.V. at the surface of the particle is less than 0.25 dL/g higher thanthe It.V. at the center of the particle, preferably less than 0.20 dL/ghigher than the It.V. at the center of the particle, preferably 0.15dL/g or less, or 0.10 dL/g or less, or even 0.050 dL/g or less. In thisembodiment, the It.V. of the polyester polymer at the surface of theparticle can be much lower than the It.V. at the center of the particle.In another embodiment, however, there is provided a polyester particlewhich has a small surface to center It.V. gradient in that the absolutevalue of the difference in the It.V. between the center of the pelletand the surface of the pellet is less than 0.25 dL/g such that thesurface It.V. can neither drop below nor exceed 0.20 dL/g relative tothe center of the particle, preferably 0.15 dL/g or less, or 0.10 dL/gor less, or even 0.50 dL/g or less. In another embodiment, in a bulk ofpellets having a volume of 1 cubic meter or more, the It.V. average ofthe differences between the It.V. of the surface of the particles andthe It.V. of the center of the particles in the bulk is not greater than0.25 dL/g, or 0.20 dL/g, or 0.15 dL/g, or 0.10 dL/g or 0.05 dL/g.

The surface of the pellet is defined as the outer 8 to 12% by mass,while the center is the inner 8 to 16% by mass around the particlecenter point. While the center point of an irregular shaped particle maybe difficult to precisely determine, it is the best approximation of theintersection between most of the straight lines that can be drawnthrough the particle between the edges or corners having the longestdistance from each other. To measure the It.V. of the surface and thecenter, a random sampling of 10 pellets from a batch is graduallydissolved according to the procedure set forth in the Examples, theweighted average of all measured cuts within the first 8-12 mass %dissolved being the surface of the pellet is recorded as It.V. surface,and the weighted average of all measured cuts within the last 8-16 mass% being the center is recorded as the It.V. center, and gradient beingthe difference between It.V. surface less the It.V. center. The numberof measurements taken within each range is not limited, and can be asfew as one measurement. The GPC method described above is used toseparately measure the It.V. of each portion dissolved. In this way, agradient starting from the surface of the particle all the way throughto the center of the particle may be measured, taking only a surface anda center cut or as many cuts throughout the particle as one desires.Alternately, the particle is sliced with a microtome, a piece of thesurface is cut away, a piece of the center is cut away, and they arethen separately measured by the GPC method described above.

Because the polyester particles having a small surface to centermolecular weight gradient undergo less It.V. loss during melt processingthan conventional polyesters, one or more advantages are envisioned. Thesubject polyester can have a lower It.V. than conventional products toobtain the same It.V. and physical properties in a molded part;therefore, manufacturing costs for the polyester are reduced. The lowerIt.V. polyester may also reduce the viscosity of the polymer during theearly stages of melt processing; hence, lower temperatures would berequired and/or energy costs would be reduced. As a result of the lowermelt processing temperatures, the acetaldehyde level in the preformswould be lower, and the time required to cool the polymer following meltprocessing would decrease as would the overall injection molding cycletime. Alternately, less drying is necessary to give the same It.V. lossas conventional polyesters; therefore, drying operational and capitalcosts are reduced.

The polymer can be produced by melt phase polymerization to a molecularweight suitable for container applications having an It.V. of at least0.70 dL/g followed by process steps comprising in no particular order:formation of particles such as pellets, crystallization, and preferablyremoval of most of the residual acetaldehyde. It is preferred to feedthe extruder for making sheet or preforms with polyester particles whichhave not been subjected to an increase in their molecular weight in thesolid state since typical solid-state polymerization processes impart anundesirably large difference in It.V. between the center of the particleand the surface of the particle. However, if the polyester has beensolid state polymerized, a small surface to center molecular weightgradient may be obtained by melting the solid stated polyester particlesand then re-forming the molten polyester into solid particles that donot have a surface It.V. that exceeds 0.03 dL/g higher than the It.V. atits center.

Thus, in another embodiment, there is provided a polyester particlehaving an It.V. of at least 0.70 dL/g obtained by melt phasepolymerization and without solid state polymerization, wherein theparticle has an It.V., a surface, and a center, wherein the It.V. at thesurface of the particle is less than 0.25 dL/g higher than the It.V. atthe center of the particle, preferably less than 0.2 dL/g higher thanthe It.V. at the center of the particle, and in yet another embodiment,said particle has an It.V. at the surface which does not vary from theIt.V. of the particle at its center by more than 0.25 dL/g.

There is also provided a process for making a polyester container,preferably a preform or beverage bottle, comprising feeding crystallizedpolyester particles having an It.V. of at least 0.70 dL/g, to anextrusion zone, melting the particles in the extrusion zone to form amolten polyester polymer composition, and forming a sheet or a moldedpart from extruded molten polyester polymer, wherein the polyesterparticles have an It.V., a surface, and a center, (and at least aportion of the polyester particles, preferably all the particles, havean It.V. at their surface which does not vary from their It.V. at theircenter by more than 0.25 dL/g, preferably by no more than 0.20 dL/g. Theparticles fed to the extrusion zone are preferably dried. The particlesdesirably have sufficient crystallinity to prevent them from sticking toeach other and/or equipment during drying at a temperature ranging from140° C. to 180° C. Moreover, the crystallized polyester particles fed tothe extrusion zone after drying preferably contain low levels ofacetaldehyde (as measured by the French National Standard Test), such as10 ppm or less, or 5 ppm or less, or even 2 ppm or less. The sheet ormolded part can be further processed to make thermoformed or blowmoldedcontainers.

Typically, polyesters such as polyethylene terephthalate are made byreacting a diol such as ethylene glycol with a dicarboxylic acid as thefree acid or its dimethyl ester to produce an ester monomer and/oroligomers, which are then polycondensed to produce the polyester. Morethan one compound containing carboxylic acid group(s) or derivative(s)thereof can be reacted during the process. All the compounds containingcarboxylic acid group(s) or derivative(s) thereof that are in theproduct comprise the “carboxylic acid component.” The mole % of all thecompounds containing carboxylic acid group(s) or derivative(s) thereofthat are in the product add up to 100. The “residues” of compound(s)containing carboxylic acid group(s) or derivative(s) thereof that are inthe product refers to the portion of said compound(s) which remains inthe oligomer and/or polymer chain after the condensation reaction with acompound(s) containing hydroxyl group(s). The residues of the carboxylicacid component refers to the portion of the said component which remainsin the oligomer and/or polymer chain after the said component iscondensed with a compound containing hydroxyl group(s).

More than one compound containing hydroxyl group(s) or derivativesthereof can become part of the polyester polymer product(s). All thecompounds containing hydroxyl group(s) or derivatives thereof thatbecome part of said product(s) comprise the hydroxyl component. The mole% of all the compounds containing hydroxyl group(s) or derivativesthereof that become part of said product(s) add up to 100. The residuesof compound(s) containing hydroxyl group(s) or derivatives thereof thatbecome part of said product refers to the portion of said compound(s)which remains in said product after said compound(s) is condensed with acompound(s) containing carboxylic acid group(s) or derivative(s) thereofand further polycondensed with polyester polymer chains of varyinglength. The residues of the hydroxyl component refers to the portion ofthe said component which remains in said product.

The mole % of the hydroxyl residues and carboxylic acid residues in theproduct(s) can be determined by proton NMR.

The polyester polymers of the invention comprise:

-   -   (a) a carboxylic acid component comprising at least 90 mole % of        the residues of terephthalic acid, derivates of terephthalic        acid, naphthalene-2,6-dicarboxylic acid, derivatives of        naphthalene-2,6-dicarboxylic acid, or mixtures thereof, and    -   (b) a hydroxyl component comprising at least 90 mole % of the        residues of ethylene glycol,        based on 100 mole percent of carboxylic acid component residues        and 100 mole percent of hydroxyl component residues in the        polyester polymer.

In another embodiment, the polyester polymer comprises:

-   -   (a) a carboxylic acid component comprising at least 92 mole %,        or at least 96 mole %, of the residues of terephthalic acid,        derivates of terephthalic acid, naphthalene-2,6-dicarboxylic        acid, derivatives of naphthalene-2,6-dicarboxylic acid, or        mixtures thereof, and    -   (b) a hydroxyl component comprising at least 92 mole %, or at        least 96 mole %, of the residues of ethylene glycol,        based on 100 mole percent of the carboxylic acid component        residues and 100 mole percent of the hydroxyl component residues        in the polyester polymer.

The reaction of the carboxylic acid component with the hydroxylcomponent during the preparation of the polyester polymer is notrestricted to the stated mole percentages since one may utilize a largeexcess of the hydroxyl component if desired, e.g. on the order of up to200 mole % relative to the 100 mole % of carboxylic acid component used.The polyester polymer made by the reaction will, however, contain thestated amounts of aromatic dicarboxylic acid residues and ethyleneglycol residues.

Derivates of terephthalic acid and naphthalane dicarboxylic acid includeC₁-C₄ dialkylterephthalates and C₁-C₄ dialkylnaphthalates, such asdimethylterephthalate and dimethyinaphthalate

In addition to a diacid component of terephthalic acid, derivates ofterephthalic acid, naphthalene-2,6-dicarboxylic acid, derivatives ofnaphthalene-2,6-dicarboxylic acid, or mixtures thereof, the carboxylicacid component(s) of the present polyester may include one or moreadditional modifier carboxylic acid compounds. Such additional modifiercarboxylic acid compounds include mono-carboxylic acid compounds,dicarboxylic acid compounds, and compounds with a higher number ofcarboxylic acid groups . Examples include aromatic dicarboxylic acidspreferably having 8 to 14 carbon atoms, aliphatic dicarboxylic acidspreferably having 4 to 12 carbon atoms, or cycloaliphatic dicarboxylicacids preferably having 8 to 12 carbon atoms. More specific examples ofmodifier dicarboxylic acids useful as an acid component(s) are phthalicacid, isophthalic acid, naphthalene-2,6-dicarboxylic acid,cyclohexanedicarboxylic acid, cyclohexanediacetic acid,diphenyl-4,4′-dicarboxylic acid, succinic acid, glutaric acid, adipicacid, azelaic acid, sebacic acid, and the like, with isophthalic acid,naphthalene-2,6-dicarboxylic acid, and cyclohexanedicarboxylic acidbeing most preferable. It should be understood that use of thecorresponding acid anhydrides, esters, and acid chlorides of these acidsis included in the term “carboxylic acid”. It is also possible fortricarboxyl compounds and compounds with a higher number of carboxylicacid groups to modify the polyester.

In addition to a hydroxyl component comprising ethylene glycol, thehydroxyl component of the present polyester may include additionalmodifier mono-ols, diols, or compounds with a higher number of hydroxylgroups. Examples of modifier hydroxyl compounds include cycloaliphaticdiols preferably having 6 to 20 carbon atoms and/or aliphatic diolspreferably having 3 to 20 carbon atoms. More specific examples of suchdiols include diethylene glycol; triethylene glycol;1,4-cyclohexanedimethanol; propane-1,3-diol; butane-1,4-diol;pentane-1,5-diol; hexane-1,6-diol; 3-methylpentanediol-(2,4);2-methylpentanediol-(1,4); 2,2,4-trimethylpentane-diol-(1,3);2,5-ethylhexanediol-(1,3); 2,2-diethyl propane-diol-(1,3);hexanediol-(1,3); 1,4-di-(hydroxyethoxy)-benzene;2,2-bis-(4-hydroxycyclohexyl)-propane;2,4-dihydroxy-1,1,3,3-tetramethyl-cyclobutane;2,2-bis-(3-hydroxyethoxyphenyl)-propane; and2,2-bis-(4-hydroxypropoxyphenyl)-propane.

The polyester pellet compositions may include blends of polyalkyleneterephthalates and polyalkylene naphthalates along with otherthermoplastic polymers such as polycarbonate (PC) and polyamides. It ispreferred that the polyester composition should comprise a majority ofthe polyester polymers, more preferably in an amount of at least 80 wt.%, or at least 95 wt. %, and most preferably 100 wt. %, based on theweight of all thermoplastic polymers (excluding fillers, inorganiccompounds or particles, fibers, impact modifiers, or other polymerswhich may form a discontinuous phase). It is also preferred that thepolyester polymers do not contain any fillers, fibers, or impactmodifiers or other polymers which form a discontinuous phase.

The polyester compositions can be prepared by polymerization proceduresknown in the art sufficient to effect esterification andpolycondensation. Polyester melt phase manufacturing processes includedirect condensation of a dicarboxylic acid with the diol, optionally inthe presence of esterification catalysts, in the esterification zone,followed by polycondensation in the prepolymer and finishing zones inthe presence of a polycondensation catalyst; or ester exchange usuallyin the presence of a transesterification catalyst in the ester exchangezone, followed by prepolymerization and finishing in the presence of apolycondensation catalyst, and each may optionally be solid statedaccording to known methods.

To further illustrate, a mixture of one or more dicarboxylic acids,preferably aromatic dicarboxylic acids, or ester forming derivativesthereof, and one or more diols are continuously fed to an esterificationreactor operated at a temperature of between about 200° C. and 300° C.,typically between 240° C. and 290° C., and at a pressure of betweenabout 1 psig up to about 70 psig. The residence time of the reactantstypically ranges from between about one and five hours. Normally, thedicarboxylic acid(s) is directly esterified with diol(s) at elevatedpressure and at a temperature of about 240° C. to about 270° C. Theesterification reaction is continued until a degree of esterification ofat least 60% is achieved, but more typically until a degree ofesterification of at least 85% is achieved to make the desired monomerand/or oligomers. The monomer and/or oligomer forming reaction(s) aretypically uncatalyzed in the direct esterification process and catalyzedin ester exchange processes.

Polycondensation catalysts may optionally be added in the esterificationzone along with esterification/ester exchange catalysts. If apolycondensation catalyst was added to the esterification zone, it istypically blended with the diol and fed into the esterification reactor.Typical ester exchange catalysts, which may be used separately or incombination, include titanium alkoxides, tin (II) or (IV) esters, ,zinc, manganese, or magnesium acetates or benzoates and/or other suchcatalyst materials that are well known to those skilled in the art.Phosphorus containing compounds and some colorants may also be presentin the esterification zone.

The resulting products formed in the esterification zone includebis(2-hydroxyethyl) terephthalate (BHET) monomer, low molecular weightoligomers, DEG, and water (or alcohol in the case of ester exchange) asthe condensation by-product, along with other trace impurities formed bythe reaction of the catalyst, if any, or starting materials and othercompounds such as colorants, impurities in the starting materials or thephosphorus containing compounds. The relative amounts of BHET andoligomeric species will vary depending on whether the process is adirect esterification process in which case the amount of oligomericspecies are significant and even present as the major species, or aester exchange process in which case the relative quantity of BHETpredominates over the oligomeric species. The water (or alcohol)isremoved as the esterification reaction (or ester exchange) proceeds todrive the equilibrium toward products. The esterification zone typicallyproduces the monomer and oligomer mixture, if any, continuously in aseries of one or more reactors. Alternately, the monomer and oligomermixture could be produced in one or more batch reactors. It isunderstood, however, that in a process for making PEN, the reactionmixture will contain monomeric species of bis(2-hydroxyethyl)naphthalate and its corresponding oligomers.

Once the ester monomer/oligomer is made to the desired degree ofesterification, it is transported from the esterification reactors inthe esterification zone to the polycondensation zone comprised of aprepolymer zone and a finishing zone. Polycondensation reactions areinitiated and continued in the melt phase in a prepolymerization zoneand finished in the melt phase in a finishing zone, after which the meltis solidified into precursor solids in the form of chips, pellets, orany other shape.

Each zone may comprise a series of one or more distinct reaction vesselsoperating at different conditions, or the zones may be combined into onereaction vessel using one or more sub-stages operating at differentconditions in a single reactor. That is, the prepolymer stage caninvolve the use of one or more reactors operated continuously, one ormore batch reactors, or even one or more reaction steps or sub-stagesperformed in a single reactor vessel. In some reactor designs, theprepolymerization zone represents the first half of polycondensation interms of reaction time, while the finishing zone represents the secondhalf of polycondensation. While other reactor designs may adjust theresidence time between the prepolymerization zone to the finishing zoneat about a 2:1 ratio, a common distinction in many designs between theprepolymerization zone and the finishing zone is that the latter zonefrequently operates at a higher temperature and/or lower pressure thanthe operating conditions in the prepolymerization zone. Generally, eachof the prepolymerization and the finishing zones comprise one or aseries of more than one reaction vessel, and the prepolymerization andfinishing reactors are sequenced in a series as part of a continuousprocess for the manufacture of the polyester polymer.

In the prepolymerization zone, also known in the industry as the lowpolymerizer, the low molecular weight monomers and oligomers arepolymerized via polycondensation to form polyethylene terephthalatepolyester (or PEN polyester) in the presence of a catalyst. If thecatalyst was not added in the monomer esterification stage, the catalystis added at this stage to catalyze the reaction between the monomers andlow molecular weight oligomers to form prepolymer and split off the diolas a by-product. Other compounds such as phosphorus-containingcompounds, cobalt compounds, and colorants can also be added in theprepolymerization zone. These compounds may, however, be added in thefinishing zone instead of or in addition to the prepolymerization zoneand esterification zone. In a typical DMT-based process, those skilledin the art recognize that other catalyst material and points of addingthe catalyst material and other ingredients vary from a typical directesterification process.

Typical polycondensation catalysts include the compounds of Sb, Ti, Ge,and Sn in an amount ranging from 0.1 to 500 ppm based on the weight ofresulting polyester polymer.

This prepolymer polycondensation stage generally employs a series of oneor more vessels and is operated at a temperature of between about 250°C. and 305° C. for a period between about five minutes to four hours.During this stage, the It.V. of the monomers and oligomers is increasedup to about no more than about 0.5 dL/g . The diol byproduct is removedfrom the prepolymer melt using an applied vacuum ranging from 4 to 70torr to drive the reaction to completion. In this regard, the polymermelt is sometimes agitated to promote the escape of the diol from thepolymer melt. As the polymer melt is fed into successive vessels, themolecular weight and thus the intrinsic viscosity of the polymer meltincreases. The pressure of each vessel is generally decreased to allowfor a greater degree of polymerization in each successive vessel or ineach successive zone within a vessel. However, to facilitate removal ofglycols, water, alcohols, aldehydes, and other reaction byproducts, thereactors are typically run under a vacuum or purged with an inert gas.Inert gas is any gas which does not cause unwanted reaction or productcharacteristics at reaction conditions. Suitable gases include, but arenot limited to argon, helium and nitrogen.

The prepolymer is fed from the prepolymer zone to a finishing zone wherethe second half of polycondensation is continued in one or morefinishing vessels generally, but not necessarily, ramped up to highertemperatures than present in the prepolymerization zone, to a valuewithin a range of from 270° C. to 305° C. until the It.V. of the melt isincreased from the It.V of the melt in the prepolymerization zone(typically 0.30 but usually not more than 0.5) to an It.V. of at least0.55. The It.V. of polyester compositions ranges from about 0.55 toabout 1.15 dL/g. Preferably, the It.V. of the polyester particles rangesfrom 0.70 dL/g to 1.15 dL/g without solid state polymerization. Thefinal vessel, generally known in the industry as the “high polymerizer,”“finisher,” or “polycondenser,” is operated at a pressure lower thanused in the prepolymerization zone, e.g. within a range of between about0.2 and 4.0 torr. Although the finishing zone typically involves thesame basic chemistry as the prepolymer zone, the fact that the size ofthe molecules, and thus the viscosity differs, means that the reactionconditions and vessel(s) may also differ. However, like the prepolymerreactor, each of the finishing vessel(s) is operated under vacuum orinert gas, and each is typically agitated to facilitate the removal ofethylene glycol, although the form of the agitation is suitable forhigher viscosities.

Additives can be added to the melt phase or to the polyester polymer toenhance the performance properties of the polyester polymer. Forexample, crystallization aids, impact modifiers, surface lubricants,denesting agents, stabilizers, antioxidants, ultraviolet light absorbingagents, metal deactivators, colorants, nucleating agents, acetaldehydelowering compounds, reheat rate enhancing aids such as elementalantimony or reduced antimony or reducing agents to form such species insitu, silicon carbide, carbon black, graphite, activated carbon, blackiron oxide, red iron oxide and the like, sticky bottle additives such astalc, and fillers and the like can be included. The resin may alsocontain small amounts of branching agents such as trifunctional ortetrafunctional carboxylic acids or their derivatives and/or alcoholssuch as trimellitic anhydride, trimethylol propane, pyromelliticdianhydride, pentaerythritol, and other polyester forming polyacids orpolyols generally known in the art. All of these additives and manyothers and their use are well known in the art and do not requireextensive discussion. Any of these compounds can be used in the presentcomposition.

The molten polymer from the melt phase polymerization may be allowed tosolidify from the melt without further crystallization. Alternatively,the molten polymer can be first solidified and then crystallized fromthe glass.

Instead of making the polyester particle directly from the melt phasepolymerization process, the particle may be made by melting postconsumer recycled polyester polymer. However, since the molecular weightof bulk recycled polyester polymers can vary widely depending on theirsource or their service requirement, it is preferred that the polyesterparticle composition comprises at least 75 wt % virgin polyesterpolymer. A virgin polyester polymer is made without post consumerrecycled polymers, but it may optionally contain scrap or regrindpolymer.

The method for solidifying the polyester polymer from the melt phaseprocess is not limited. For example, molten polyester polymer from themelt phase may be directed through a die, or merely cut, or bothdirected through a die followed by cutting the molten polymer. A gearpump may be used as the motive force to drive the molten polyesterpolymer through the die. Instead of using a gear pump, the moltenpolyester polymer may be fed into a single or twin screw extruder andextruded through a die, optionally at a temperature of 190° C. or moreat the extruder nozzle. Once through the die, the polyester polymer canbe drawn into strands, contacted with a cool fluid, and cut intopellets, or the polymer can be pelletized at the die head, optionallyunderwater. The polyester polymer melt is optionally filtered to removeparticulates over a designated size before being cut. Any conventionalhot pelletization or dicing method and apparatus can be used, includingbut not limited to dicing, strand pelletizing and strand (forcedconveyance) pelletizing, pastillators, water ring pelletizers, hot facepelletizers, underwater pelletizers and centrifuged pelletizers.

The method and apparatus used to crystallize the polyester polymer isnot limited, and includes thermal crystallization in a gas or liquid.The crystallization may occur in a mechanically agitated vessel; afluidized bed; a bed agitated by fluid movement; an un-agitated vesselor pipe; crystallized in a liquid medium above the T_(g) of thepolyester polymer, preferably at 140° C. to 180° C.; or any other meansknown in the art. Also, the polymer may be strain crystallized.

It is desirable to crystallize the pellets to at least a 15% degree ofcrystallization, more preferably to at least 25%, or at least 30%, or atleast 35%, or at least 40%.

Pellet crystallinity is determined using Differential ScanningCalorimetry (DSC). The sample weight for this measurement is 10±1 mg andthe sample consists of either (1) a portion of a single pellet, or morepreferably (2) a sample taken from several grams of cryogenically groundpellets. The first heating scan is performed. The sample is heated fromapproximately 25° C. to 290° C. at a rate of 20° C./minute, and theabsolute value of the area of the melting endotherms (one or more) minusthe area of any crystallization exotherms is determined. This areacorresponds to the net heat of melting and is expressed in Joules. Theheat of melting of 100% crystalline PET is taken to be 119 Joules/gram,so the weight fraction crystallinity of the pellet is calculated as thenet heat of melting divided by 119. Unless otherwise stated, the initialmelting point in each case is also determined using the same DSC scan.

The percent crystallinity is calculated from both of:

-   -   Low peak melting point: T_(m1a)    -   High peak melting point: T_(m1b)

Note that in some cases, particularly at low crystallinity,rearrangement of crystals can occur so rapidly in the DSC instrumentthat the true, lower melting point is not detected. The lower meltingpoint can then be seen by increasing the temperature ramp rate of theDSC instrument and using smaller samples. A Perkin-Elmer Pyris-1calorimeter is used for high-speed calorimetry. The specimen mass isadjusted to be inversely proportional to the scan rate. About a 1 mgsample is used at 500° C./min and about 5 mg are used at 100° C./min.Typical DSC sample pans were used. Baseline subtraction is performed tominimize the curvature in the baseline.

Alternatively, percent crystallinity is also calculated from the averagegradient tube density of two to three pellets. Gradient tube densitytesting is performed according to ASTM D 1505, using lithium bromide inwater.

Once the pellets are crystallized to the desired degree, they aretransported to a machine for melt processing into the desired shape,such as sheets for thermoforming into trays or preforms suitable forstretch blow molding into beverage or food containers. Examples ofbeverage containers include containers having a volume of 3 liters orless, suitable for hot fill, carbonated soft drinks, or water.

Thus, there is also provided the process for making a container such asa tray or a bottle preform suitable for stretch blow molding comprisingdrying PET pellets having an It.V. ranging from 0.7 to 1.15 dL/g and asmall surface to center molecular weight gradient in a drying zone at azone temperature of at least 140° C., introducing the dried pellets intoan extrusion zone to form a molten PET polymer composition, and forminga sheet or a molded part from extruded molten PET polymer.

In this embodiment, the pellets which are prepared for introduction intoan extruder are preferably not solid stated, or if solid stated havebeen re-melted and solidified to yield a desired small surface to centermolecular weight gradient. These polyester particles have an It.V.sufficiently high such that the physical properties are suitable for themanufacture of bottle preforms and trays. The non-solid stated highIt.V. pellets have been sufficiently crystallized to prevent them fromsignificantly agglomerating in the dryer at temperatures of 140° C. ormore, and up to about 190° C., or 180° C. Dryers feeding melt extrudersare needed to reduce the moisture content of pellets. Moisture in or onpellets fed into a melt extrusion chamber will cause the melt to loseIt.V. at melt temperatures by hydrolyzing the ester linkages with aresulting change in the melt flow characteristics of the polymer andstretch ratio of the preform when blown into bottles. Therefore, priorto extrusion the pellets are dried at a temperature of 140° C. or moreto drive off most all of the moisture on and in the pellet, meaning thatthe temperature of the heating medium (such as a flow of nitrogen gas orair) is 140° C. or more. It is desirable to dry the pellets at hightemperatures of 140° C. or more to decrease the residence time of thepellets in the dryer and increase throughput.

To dry at high temperatures while minimizing agglomeration in aconventional dryer equipped with or without an agitator, the pelletsshould be crystallized at 140° C. or more. In general, the typicalresidence time of pellets in the dryer at conventional temperatures(140° C. to 190° C.) will on average be from 0.75 hours to 8 hours. Anyconventional dryer can be used. The pellets may be contacted with a flowof heated air or inert gas such as nitrogen to raise the temperature ofthe pellets and remove volatiles from inside the pellets, and may alsobe agitated by a rotary mixing blade or paddle. The flow rate of theheating gas, if used, is a balance between energy consumption, residencetime of pellets, and preferably avoiding the fluidization of thepellets. Suitable gas flow rates range from 0.05 to 100 scfm for everypound per hour of pellets discharged from the dryer, preferably from 0.2to 5 scfm per lb/hr of pellets.

Once the pellets have been dried, they are introduced into an extrusionzone to form molten polyester polymer, followed by processing the moltenpolymer to form a molded part, such as a bottle preform (parison)through injecting the melt into a mold or extruding into a sheet orcoating. Methods for the introduction of the dried pellets into anextrusion zone, for melt processing, injection molding, and sheetextrusion are conventional and known to those of skill in themanufacture of such containers. Extruder barrel temperatures rangingfrom 260° C. to 305° C. are suitable for processing the polyesterparticles of the invention.

At the extruder, or in the melt phase for making the polyester polymer,other components can be added to the composition of the presentinvention to enhance the performance properties of the polyesterpolymer. These components may be added neat to the bulk polyester, mayadded as a dispersion in a liquid carrier or may be added to the bulkpolyester as a polyester concentrate containing at least about 0.5 wt. %of the component in the polyester let down into the bulk polyester.

The types of suitable components include crystallization aids, impactmodifiers, surface lubricants, stabilizers, denesting agents,antioxidants, ultraviolet light absorbing agents, metal deactivators,colorants, nucleating agents, acetaldehyde lowering compounds, reheatrate enhancing aids, sticky bottle additives such as talc, and fillersand the like can be included. The resin may also contain small amountsof branching agents such as trifunctional or tetrafunctional comonomerssuch as trimellitic anhydride, trimethylol propane, pyromelliticdianhydride, pentaerythritol, and other polyester forming polyacids orpolyols generally known in the art. All of these additives and manyothers and their use are well known in the art and do not requireextensive discussion. Any of these compounds can be used in the presentcomposition.

Not only may containers be made from pellets made according to theprocess of this invention, but other items such as sheet, film, bottles,trays, other packaging, rods, tubes, lids, filaments and fibers, andother injection molded articles may also be manufactured using thepolyester particles of the invention. Beverage bottles made frompolyethylene terephthalate suitable for holding water or carbonatedbeverages, and heat set beverage bottle suitable for holding beverageswhich are hot filled into the bottle are examples of the types ofbottles which are made from the crystallized pellet of the invention.

The invention may now be further understood by reference to thefollowing non-limiting illustrative examples.

EXAMPLES

The method for determining the molecular weight gradient throughout thepellets was as follows. 10 pellets having a combined mass of 0.20±0.06gram were placed in a small stainless steel wire mesh basket. The basketwas placed into a small flask containing 3 to 4 mL of stirred GPCsolvent (70% hexafluoroisopropanol, 30% methylene chloride) such thatthe pellets were immersed in the solvent. After a period of timeappropriate for the dissolution rate of the pellets (about 2 minutes forthe pellets of Examples 2 and 4 and 10 minutes for the pellets ofComparative Examples 1 and 3) the basket was removed from the flask.This caused the outer layer of the pellets to become dissolved in theGPC solvent. The procedure was sequentially repeated using fresh solventfor each cycle until the pellets were completely dissolved. The solutionfrom each dissolution cycle (“cut”) was diluted with additional GPCsolvent to increase the volume to 10.0 mL. The molecular weightdistribution of each “cut” was measured by injecting 10 μL into the GPC.The It.V. was calculated from the <M>_(w) using the relations givenabove. The mass of polymer present in each “cut” was calculated as thechromatogram peak area for that “cut” divided by the total chromatogrampeak area for all of the “cuts” of that sample.

Other than the It.V. values reported for determining the molecularweight gradient, reported It.V. values are determined by the solutionviscosity method.

Comparative Example 1

Conventional solid stated pellets commercially available from EastmanChemical Company as PET CB11 E were dried in a commercial-scaledesiccant-air dryer. The temperature in the primary dryer hopper (5.5hour pellet residence time) was 175° C. and the temperature in thesecondary dryer hopper (2 hours residence time) was 185° C. The pelletshad a degree of crystallinity of about 47% by weight as measured by DSC.The It.V. of the dried pellets was 0.803 dL/g. The It.V. differencebetween the center and surface (the pellet It.V. gradient) was measuredaccording to the procedures described above and the results are given inTable 1. TABLE 1 It.V. Gradient for the Pellets of Comparative Example 1Cumulative Weight It.V. Fraction Calculated Cut Dissolved <M>_(w) from<M>_(w) 1 0.090 71794 0.976 (surface) 2 0.168 62511 0.881 3 0.245 581670.836 4 0.318 55094 0.803 5 0.394 52909 0.780 6 0.475 50790 0.757 70.522 50210 0.750 8 0.575 49440 0.742 9 0.620 48601 0.733 10  0.68347826 0.725 11  0.719 47403 0.720 12  0.820 46720 0.712 13  0.847 463140.708 14  1.000 44861 0.692 (center)

The results show that the It.V. of the surface cut (Cut 1, outer 9.0% byweight of the pellets) was 0.976 and that the It.V. of the center cut(Cut 14, center 15.3% by weight of the pellets) was about 0.692. Thiscorresponds to an It.V. difference of 0.284 between the surface andcenter of the pellets.

The dried pellets were melt processed into preforms using acommercial-scaling injection molding machine for making the preforms.The temperature of the molding machine extruder barrel zones ranged from275° C. to 295° C. The It.V. of the preforms was 0.759 dL/g. Meltprocessing caused the It.V. to be reduced by 0.044 dL/g.

Example 2

Polyester pellets having a similar chemical composition to the pelletsof Example 1 had an It.V. of 0.831 dL/g (solution viscosity) afterdrying under the same conditions as described in Example 1. The pelletshad a degree of crystallinity of about 36.5% by weight as measured byDSC and were not solid stated. The It.V. gradient between the center andsurface was measured according to the procedures described above. Table2 sets forth the results of the measurements. TABLE 2 It.V. Gradient forthe Pellets of Example 2 Cumulative It.V. Weight Calculated Fractionfrom Cut Dissolved <M>_(w) <M>w 1 0.102 57351 0.827 (surface) 2 0.30057576 0.829 3 0.444 58347 0.838 4 0.595 57871 0.832 5 0.691 58300 0.8376 0.791 57608 0.830 7 0.850 59243 0.847 8 0.901 59208 0.847 9 0.93658596 0.840 10  0.970 59493 0.849 11  1.000 59128 0.846 (center)

The results show that the It.V. of the surface cut (Cut 1, outer 10.2%by weight of the pellets) was 0.827 and that the It.V. of the centercuts (Cuts 8-11, center 15.0% by weight of the pellets) was about 0.847.This corresponds to an It.V. difference of 0.020 between the surface andcenter of the pellets.

The dried pellets were melt processed into preforms using the sameconditions as described in Example 1. The It.V. of the preforms was0.812 dL/g. Melt processing caused the It.V. to be reduced by 0.019dL/g, less than 50% of the It.V. reduction experienced by theconventional pellets of Example 1.

Comparative Example 3

Conventional solid-state polymerized pellets commercially available fromEastman Chemical Company as Voridian CB12 solid stated to an It.V.(before drying) of 0.850 were dried in a small dryer (approximately 40pounds capacity) at 150° C. for 6 hours. The pellets had a degree ofcrystallinity of about 48% by weight as measured by DSC. The It.V.difference between the center and surface (the pellet It.V. gradient)was measured according to the procedures described above and the resultsare given in Table 3. TABLE 3 It.V. Gradient for the Pellets ofComparative Example 3 Cumulative Weight It.V. Fraction Calculated CutDissolved <M>_(w) from <M>_(w) 1 0.083 80992 1.067 (surface) 2 0.14373439 0.992 3 0.212 67237 0.930 4 0.340 61829 0.874 5 0.467 57023 0.8236 0.608 54777 0.800 7 0.737 51950 0.769 8 0.862 50299 0.751 9 0.90450609 0.754 10  0.952 49795 0.746 11  0.977 49063 0.738 12  1.000 484590.731 (center)

The results show that the It.V. of the surface cut (Cut 1, outer 8.3% byweight of the pellets) was 1.067 and that the It.V. of the center cuts(Cuts 9-12, center 13.8% by weight of the pellets) was about 0.744. Thiscorresponds to an It.V. difference of 0.323 between the surface andcenter of the pellets.

The dried pellets were melt processed into preforms using alaboratory-scale injection molding machine. The temperature of themolding machine extruder barrel was 285° C. The It.V. of the preformswas 0.801 dL/g. Melt processing caused the It.V. to be reduced by 0.049dL/g.

Example 4

Polyester pellets from the same batch as those used in Example 2 weredried and melt processed into preforms using the same conditions asdescribed in Example 3. These pellets had an It.V. (before drying) of0.830 and less difference (<0.2 dL/g) between the It.V. of the centerand surface of the pellet. The It.V. of the preforms was 0.810 dL/g.Melt processing caused the It.V. to be reduced by 0.020 dL/g, less than50% of the It.V. reduction experienced by the conventional pellets ofExample 3.

1. A polyester polymer particle comprising a polyester polymer comprising: (a) a carboxylic acid component comprising at least 90 mole % of the residues of terephthalic acid, derivates of terephthalic acid, naphthalene-2,6-dicarboxylic acid, derivatives of naphthalene-2,6-dicarboxylic acid, or mixtures thereof, and (b) a hydroxyl component comprising at least 90 mole % of the residues of ethylene glycol, based on 100 mole percent of the carboxylic acid component residues and 100 mole percent hydroxyl component residues in the polyester polymer, wherein said particle has an It.V. of at least 0.70 dL/g , and the It.V. at the surface of the particle is less than 0.25 dL/g higher than the It.V. at the center of the particle.
 2. The particle of claim 1, wherein the particle has an It.V. of at least 0.74 dL/g.
 3. The particle of claim 2, wherein the particle has an It.V. of at least 0.77 dL/g.
 4. The particle of claim 2, wherein the It.V at the surface of the particle is less than 0.2 dL/g higher than the It.V. at the center of the particle.
 5. The particle of claim 1, wherein the It.V. at the surface of the particle is less than 0.15 dL/g higher than the It.V. at the center of the particle.
 6. The particle of claim 1, wherein the particle has a degree of crystallinity of at least 25%.
 7. The particle of claim 1, wherein the particle contains less than 10 ppm acetaldehyde.
 8. Polyester particles having a number average weight of at least 1.0 g per 100 particles, wherein each particle is the polyester particle of claim
 1. 9. The polyester particle of claim 1, wherein said polyester particle is a virgin polyester polymer.
 10. The polyester particle of claim 1, wherein the polyester polymer contains at least: (a) a carboxylic acid component comprising at least 92 mole % of the residues of terephthalic acid, or derivates of terephthalic acid, or mixtures thereof, and (b) a hydroxyl component comprising at least 92 mole % of the residues of ethylene glycol, based on 100 mole percent of the polycarboxylic acid component residues and 100 mole percent hydroxyl component residues in the polyester polymer.
 11. The particle of claim 1, wherein the It.V. of the particle at the surface does not vary from the It.V. of the particle at its center by more than 0.10 dL/g.
 12. The particle of claim 11, wherein the It.V. of the particle at the surface does not vary from the It.V. of the particle at its center by more than 0.20 dL/g.
 13. The particle of claim 11, wherein the polyester polymer contains at least: (a) a carboxylic acid component comprising at least 96 mole % of the residues of terephthalic acid, or derivates of terephthalic acid, or mixtures thereof, and (b) a hydroxyl component comprising at least 96 mole % of the residues of ethylene glycol, based on 100 mole percent of the carboxylic acid component residues and 100 mole percent hydroxyl component residues in the polyester polymer.
 14. The particle of claim 13, wherein the particle has a degree of crystallinity of at least 25%.
 15. The particle of claim 1, comprising a bulk of said particles having a volume of at least 1 cubic meter.
 16. The particle of claim 15, wherein the It.V. average of the differences between the It.V. of the surface of the particles and the It.V. of the center of the particles in the bulk is not greater than 0.20 dL/g.
 17. The particle of claim 16, wherein the It.V. average of the differences is not greater than 0.10 dL/g.
 18. A blow molded container obtained from the polyester polymer particles of any one of claims 1 through
 17. 19. A beverage bottle obtained from the polyester polymer particles of claim
 1. 20. A polyester particle having a degree of crystallinity of at least 25% and an It.V. of at least 0.70 dL/g , said particle having an It.V. at its surface and an It.V. at its center, wherein the It.V. at the surface of the particle is less than 0.25 dL/g higher than the It.V. at the center of the particle.
 21. The particle of claim 20, wherein the polyester polymer contains: (a) a carboxylic acid component comprising at least 90 mole % of the residues of terephthalic acid, or derivates of terephthalic acid, or mixtures thereof, and (b) a hydroxyl component comprising at least 90 mole % of the residues of ethylene glycol, based on 100 mole percent of the carboxylic acid residues and 100 mole percent hydroxyl residues in the polyester polymer.
 22. The polyester particle of claim 21, wherein the degree of crystallinity is at least 35%, and the It.V. of the particle is at least 0.74 dL/g.
 23. The polyester particle of claim 21, wherein the difference between the It.V. of the particle at its surface and its center is 0.15 dL/g or less.
 24. The polyester particle of claim 23, wherein the difference is 0.05 dL/g or less.
 25. A blow molded container obtained from the polyester particles of claim 1 having an degree of crystallinity of at least 35%, and an It.V. of at least 0.77 dL/g, said blow molded container obtained without increasing the molecular weight of the pellets by solid state polymerization.
 26. A process for making a container from a polyester(s) polymer, comprising feeding polyester particles having a degree of crystallinity of at least 15% and an It.V. of at least 0.70 dL/g to an extrusion zone, melting the particles in the extrusion zone to form a molten polyester polymer composition, and forming a sheet or a molded part from extruded molten polyester polymer, wherein the polyester particles fed to the extrusion zone have an It.V. at their surface which is less than 0.25 dL/g higher than the It.V. at their center.
 27. The process of claim 26, wherein the It.V. at the surface of the particles is less than 0.20 dL/g higher than the It.V. at the center of the particles.
 28. The process of claim 27, wherein the wherein the difference between the It.V. of the particles at their surface and their center is 0.10 dL/g or less.
 29. The process of claim 28, wherein the difference is 0.05 dL/g or less.
 30. The process of claim 26, wherein the molded part is a container preform.
 31. The process of claim 30, comprising stretch blow molding the preform into a beverage container.
 32. The process of claim 31, wherein the container has a volume of 3 liters or less.
 33. The process of claim 27, comprising drying the particles in a drying zone at temperature of at least 140° C. before melting the particles in the extrusion zone.
 34. The process of claim 26, further comprising drying the particles before feeding the particles to the extrusion zone, wherein the particles are not solid state polymerized before drying.
 35. The process of claim 34, wherein the particles have an acetaldehyde level of 10 ppm or less prior to melting in the extrusion zone.
 36. The process of claim 26, wherein the polyester polymer particles comprise: (a) a carboxylic acid component comprising at least 90 mole % of the residues of terephthalic acid, or derivates of terephthalic acid, or mixtures thereof, and (b) a hydroxyl component comprising at least 90 mole % of the residues of ethylene glycol, based on 100 mole percent of the carboxylic acid component residues and 100 mole percent hydroxyl component residues in the polyester polymer, and at least 75% of the polyester polymer is virgin polymer.
 37. The process of claim 36, wherein the polyester polymer particles comprises: (a) a carboxylic acid component comprising at least 92 mole % of the residues of terephthalic acid, or derivates of terephthalic acid, or mixtures thereof, and (b) a hydroxyl component comprising at least 92 mole % of the residues of ethylene glycol, based on 100 mole percent of the carboxylic acid component residues and 100 mole percent hydroxyl component residues in the polyester polymer.
 38. The process of claim 37, wherein the degree of crystallinity is at least 25%.
 39. The process of claim 26, wherein the degree of crystallinity is at least 35%.
 40. The process of claim 26, comprising a bulk of said particles having a volume of at least 1 cubic meter.
 41. The particle of claim 40, wherein the It.V. average of the differences between the It.V. of the surface of the particles and the It.V. of the center of the particles in the bulk is not greater than 0.20 dL/g.
 42. The particle of claim 41, wherein the It.V. average of the differences is not greater than 0.10 dL/g.
 43. A blow molded container obtained from the particles of claim
 26. 44. A preform obtained from the particles of claim
 26. 45. Polyester particles having a particle weight of greater than 1.0 g per 100 particles and less than 100 g per 100 particles, said particles, comprising at least 75% virgin polyester polymer, comprising: (a) a carboxylic acid component comprising at least 90 mole % of the residues of terephthalic acid, or derivates of terephthalic acid, or mixtures thereof, and (b) a hydroxyl component comprising at least 90 mole % of the residues of ethylene glycol, based on 100 mole percent of the carboxylic acid component residues and 100 mole percent hydroxyl component residues in the polyester polymer, the particles having a degree of crystallinity of at least 25%, an It.V. of at least 0.77 dL/g, an It.V. at their surface and an It.V. at their center wherein the It.V. at the surface of the particles is not greater than 0.15 dL/g higher than the It.V. at the center of the particles, and having an acetaldehyde level of 10 ppm or less.
 46. The particles of claim 45, wherein the particles comprise a bulk having a volume of at least 1.0 cubic meter.
 47. The particles of claim 46, wherein in the It.V. average of the differences between the It.V. of the surface of the particles and the It.V. of the center of the particles in the bulk is not greater than 0.15 dL/g.
 48. The particles of claim 47, wherein the It.V. average of the differences is not greater than 0.10 dL/g.
 49. The particles of claim 48, wherein the It.V. average is not greater than 0.05 dL/g.
 50. A blow molded container obtained from the particles of claim
 45. 51. A beverage bottle obtained from the particles of claim
 45. 52. A perform obtained from the particles of claim 45 